Boston — A small, hibernating brown bat with a big appetite for bugs – including farm pests and mosquitoes – is in danger of going extinct in the American Northeast.

Scientists say that a fungus is to blame for killing the bats and could wipe out the population within 16 years unless ways can be found to control the fungus.

That's the conclusion a team of biologists has reached after calculating the potential effects on the bat population of a significant die-off that has emerged in the four years since the fungus was first spotted.

A recreational caver captured the first images of the telltale whitened bats' noses in Howe Caverns, a popular tourist destination 34 miles west of Albany, N.Y. Since then, the fungus associated with "white-nose syndrome" has been detected among bats in at least 115 locations from Ontario to Tennessee where the creatures hibernate for the winter.

Faint rays of hope are appearing on the horizon for at least buying time for the little brown myotis bat. But for now, the prospect of decimation looms large.

Although the study, published in today's issue of the journal Science, involves only one species of bat, biologists have detected the fungus in nine species, says Thomas Kunz, who heads the Bat Lab at Boston University's Center for Ecology and Conservation Biology.

Trouble in the bat cave

The study grew out of the increasing number of reports from Northeastern wildlife biologists of cave floors littered with dead bats, all displaying evidence of having picked up the fungus. For the first two years bats were observed to host the fungus, they seemed little affected. By the third and fourth years, however, huge die-offs occurred.

The team found that populations of little brown myotis in the 115 hibernation locations the study covered were falling at rates ranging from 33 percent to 99 percent per year, with an average decline for the Northeast of 73 percent each year.

Slightly more than 1 million bats have vanished in the past two years, the team estimates. The team calculates that out of an initial population of some 6.5 million bats, the little-brown-myotis population could fall as low as 65,000 by 2026.

If the fungus expands farther south and west, the bats' disappearance could result in unpredictable changes to ecosystems. For example, given the bats' rate of bug consumption, the casualties so far would have consumed about 694 tons of insects in one warm season.

Once bats pick up the fungus, they become a major carrier to other locations. But the lead suspect in introducing the disease to North America is human transportation – fungal spores carried on clothing or shoes contaminated in Europe, where a genetically identical fungus is known to thrive in caves where bats hibernate.

As a result, wildlife managers are closing some caves to tourists and recreational cavers. Some caves with heavy tourist traffic require visitors to undergo simple shoe-disinfectant procedures, researchers say.

European bats immune

A team of German, Swiss, and US researchers found that several species of hibernating bats in Europe carry the fungus but are not suffering any effects from it.

The team suggests that either the bats' behavior or immunity from long exposure to the fungus accounts for the lack of fatalities in Europe's caves. Although none of the bats studied in Europe are the same species as the afflicted bats in the US, some belong to the same genus, which may be helpful in making cross-Atlantic comparisons.

In the meantime, one of two study sites in Massachusetts is giving some cause for hope says Dr. Kunz, who also took part in the new study. Since May, a summer colony in Paxton, Mass., appears to have stabilized, after a significant decline between 2008 and 2009.

"It's a small sample size," he says, "but it's a hopeful sign there are survivors out there."